Laser ablation is one of the non-traditional methods of materials processing that may substantially alter the physical properties of samples. In addition to removing atoms from the surface, it may leave behind a recrystallized surface layer of altered composition and properties.
For example, lasers have been used to change the crystalline structure of graphite to form diamonds. M. C. Polo, J. Cirfe et al., “Pulsed laser deposition of diamond from graphite targets,” Appl. Phys. Lett., Vol. 67, No. 4, p. 435 (24 Jul. 1995). P. S. Banks, B. C. Stuan et al., “Short Pulse laser Production of Diamond Thin Films,” UCRL-ID-130327 (Mar. 20, 1998). M. D. Shink, P. A. Motian, “Ultra-short pulsed laser ablation of highly oriented pyrolytic graphite,” Carbon, Vol. 39, pp. 1183-1193 (2001). Adam Mechler et al., “Excimer laser irradiation induced formation of diamond-like carbon layer on graphite,” Applied Surface Science, Vol. 138-139, pp. 174-178 (1999).
Oxygen content is known to affect layered cuprate superconductors. For example, for YBa2Cu3O6+δ, relatively small variations of oxygen can shift this material's properties from a dielectric to a superconductor. Yoichi Ando, et al, “Electronic Phase Diagram of High-Tc, Cuprate Superconductors,” Physical Review Letters, PRL 93, 267001 (Dec. 31, 2004). Another, isostructural example, is Sr2CuO4−δ, which is known as a semiconductor at δ=0.1. See R. C. Lobo, F. J. Berry, and C. Greaves, “The synthesis and structural characterization of Sr2CuO4−x, x˜0.1”, J. Solid State Chem., Vol. 88, pp. 513-519 (1990). Sr2CuO4−δ exhibits superconductivity at 50K when oxygen is enhanced. See S. Karimoto, H. Yamamoto, H. Sato, A. Tsukada, and M. Naito, “Tc versus lattice constants in MBE-grown M2CuO4 (M=La, Sr, Ba),” J. Low Temp. Phys., Vol. 131, pp. 619-623 (2003). The ability of copper to take on different valences plays a role in allowing these modified species to exist. Similarly, ruthenium is known to have valences higher than +4, while strontium can have only a valence of +2. At the same time compounds are known, for example, RuO4, where the valence of ruthenium is +8, and intermediate valences are also possible. Previous attempts to enhance the oxygen content of Sr2RuO4 appear to be largely unsuccessful. A. P. Mackenzie, Y. Maeno, “The superconductivity of Sr2RuO4 and the physics of spin-triplet pairing,” Rev. Mod. Phys., Vol. 75, pp. 657-712 (2003). Perhaps, this was because equilibrium thermodynamic approaches were used in those attempts.